A position measuring method or position measuring system is known from DE 199 54 328 A1. There a waveguide is present in the longitudinal direction of which an object coupled with a magnet can be slid. A torsion wave is generated in the waveguide on the basis of an excitation pulse striking upon the magnetic field of the magnet. A reel is provided to derive a reply pulse from the torsion wave. The position of the object along the wave guide is inferred from the time between the excitation pulse and the reply pulse.
The excitation pulse is triggered by an external interrogation pulse with which the position of the object is queried. Since after the interrogation pulse arrives a certain period of time is necessary for conducting the previously described ascertainment of the position of the object, the ascertained position is calculated in advance at the current point in time of the interrogation pulse. For this, the last ascertained and stored positions of the object are adduced and taken into consideration, for example using linear extrapolation.
Owing to the non-linear character of the waveguide, the position calculated beforehand must be corrected. For this, a table is present in DE 199 54 328 A1, in which an associated correction factor is contained at any ascertained position. The correction factors are moreover determined from the start using highly exact measurements of positions of the object. The correction factors relate to the ascertained positions of the object and consequently correct this result of the known position measuring system.
The position of the object corrected in this way is finally converted into a period of time and output with the aid of a start and a stop impulse.
The disadvantage of the described magnetostrictive position measuring method or system includes among other things in that the minimum period of time in which interrogation pulses can be processed depends upon the time necessary for correction of the ascertained position.